Minimum Slope For Flat Roof

In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory.

Minimum slope for flat roof.

The short simple answer is 2 12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. In order to achieve this drop a slightly steeper angle of 1 40 1 44 should be the aim when installing a flat roof as this accounts for surface deviations and material deflection among other things. The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems. It takes the manufacturer s recommendations the unique conditions of the roof as well as the skills and the expertise of the installer to arrive at the right slope.

This means for every 12 horizontal units the roof must rise a minimum of 3 vertical units. Normally 1 80 0 72 is the recommended minimum angle for a slope and this is universal across the vast majority of flat roofing systems regardless of the materials that they incorporate. Asphalt shingles continue to be the most widely installed roof covering option in north america. For example the international building code 2018 edition ibc 2018 prescribes a 1 4 12 minimum roof slope for asphalt built up polymer modified bitumen thermoset and thermoplastic single ply and liquid applied membranes in new construction.

The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code.